Many types of ground drilling systems are available for drilling holes for particular purposes and in specific ground conditions. One range of down hole drill systems utilise a fluid under pressure to assist in advancing the drill. The fluid may act to either drive a drilling tool coupled to an associated drill string, or to flush drill cuttings from a hole being drilled, or both. The fluid can be gas such as air or nitrogen, a liquid/slurry such as water or drilling mud, or a combination of gas and liquid.